Method of growing synthetic quartz



April 1960 'r. J. TUROBINSKI 2,931,712

METHOD OF GROWING SYNTHETIC QUARTZ Filed May 27, 1955 INVENTOR. ATHADDEUS J.TUROB|NSK| igs) ATTORNEY METHOD GROWENG SYNTHETIC QUARTZThaddeus .i. Turohinski, Cleveland Heights,- Ohio, assignor to CleviteCorporation, Cleveland, Ohio, a corporation of Ghio Application May 27,1955, Serial No. 511,667

2 Claims. (11. 23-301 the copending application of Hans Jatle andThaddeus I. Turobinski, Serial No. 459,052, filed September 29, 1954,and assigned to the same assignee a's the present invention. A i

' In the following specification the Standards on Piezoelectric Crystals(1949) of the Institute of Radio Engineers as set forth in theProceedings of the I.R.E., vol. 37, pp. 1378-1395, are adhered to. i 1

Broadly speaking, a Y-bar seed is one which is elongated in thedirection of the Y crystal axis and has a width and thickness, i.e.,cross-sectional dimensions, much smaller than its length, for example,in the ratio of l to 20 or more. A Y-bar crystal is one grown from'Y-bar seed and is similar in length to the seed but larger in the otherdimensions.

The term extra-length or extended is used herein to describe Y-bar seedsand/or crystals having a length in the direction of the Y-crystal axisexceeding that which it has been possible to obtain heretofore inelectronically useful quality from either natural or synthetic quartzcrystals.

As set forth in detail in the aforementioned applica- -tion, quartzcrystal plates have for many years been used extensively asfrequency-controlling elements in-r'adio frequency oscillators,electrical filters, and the'like. In consequence of the continuing andgrowing requirements of the electronics industry for such plates muchresearch and development work has been performed in an effort to evolvemethods and appparatus for synthesizing large single crystals of quartzfrom which such plates may be fabricated.

Among the more important recent advances in the quartz crystal growingfield wasthe discovery and development of the Y-bar seed fully disclosedin the abovementioned application.

The length of the Y-bar seed (within the limits imposed by availabilityas hereinafter explained) and the period of crystal growth are soselected thatthe resulting Y-bar crystal is characterized by a uniqueand highly advantageous configuration in which the primary prism faces,which retard growthand render large sections of ordinary quartz crystalsunusuable for cutting into plates, develop only to a moderate extentduring the growing period. Consequently, Y-bar crystals properly grownaccording to the disclosure of the aforesaid Letters Patent No.2,923,605 are elongated in the direction of the Y crystal axis andpossess an intermediate portion of substantially rectangularcross-section i'n the plane of the X and 2 crystal axes, which portionextends for about 4 inches of the customary 6 inch length of suchcrystals.

'Thus the intermediate portion of the Y-bar crystalap proximates aregularly shaped block or rectangular parallelepiped of quartz about 4inches long practically all of. which is usable for crystal plateblanks;-for example, the entire block may be cut along spaced parallelplanes disposed at an angle of about 35 15' to the Z crystal axis toobtain the extensively used AT plates.

While the Y-bar seed and the crystals grown therefrom are significantimprovements over previously known seeds and crystal shapes as regardsthe proportion of usable quartz in a crystal, the ratio of crystal toseed weight, and the number of crystal plate blanks that can be cut froma single crystal, there is still room for considera ble improvement inthe way of increased yields of usable material and decreased productioncosts.

The length of the Y-b'ar seed available up to the time of the presentinvention extending as it does transverse- 1y to the '2 crystal axis,that is, between opposite m faces of the single crystal from which it iscut, is limited by the relatively small dimension of a single quartzcrystal in the direction of the Y crystal axis. Since natural quartzcrystals of electronic grade, as well as those synthetically produced,having a dimension of more than six inches in the Y direction are rare,they are correspondingly expensive, costing hundreds or thousands ofdollars for a single good specimen. Crystals of electronically usefulquality having a Y axis dimension much in excess of eight inches arehardly obtainable at any price. The foregoing factors have concomitantlylimited the length of available Y-bar seeds to approximately six inches.

In a crystal 6 inches long, the usable intermediate portion is onlyabout 4 inches in length. The ends of the crystal, representing about /3its total length, develop the characteristic rhombohedral faces duringthe growing process and consequently, much of this must be trimmed asscrap.

painstaking set-up work in order to cut up a block of material only' 4inches long; the entire procedure must be repeated for each crystal tobe cut into plates.

Another handicap characterizing the present production ofsynthetic-quartz crystals is the fact that each seed mustbe individuallyloaded into a seed holder for,placement in an autoclave, for example, asdescribed in United States Letters Patent No. 2,675,303 granted toAndrew Sobek and Danforth R. Hale and assigned to the same assignee asthe present invention. Inasmuch as production considerations requirelarge autoclaves and presently obtainable seeds are only 6 to 8 inchesin length, a

single run may require the loading of 200 or more individual seeds intosuitable holders.

In accordance with the present invention the difficulties anddisadvantages outlined above are overcome by the provision and use of anovel, and improved Y-bar" quartz. seed which is limited in lengthsolely by pracproperly oriented, to grow a single Y-bar crystal ofextended length. which may be used as a source of seedto grow additionalextra-length seed material and/or crystals.

More specifically extra-length crystals of quartz are obtained accordingto the present invention from two .or

more Y-bar s eed s placed in end-to-end contact with their correspondingatomic planes aligned; splinting' the joint cut from the same mothercrystal.

between the seeds with crystal so as to preclude relative movementtherebetween; and exposing the seeds, s'o splinted, to a chemical andphysical environment conducive to crystal growth, as hereinafterdescribed in detail.

With the foregoing state of the art in view, it is a fundamental objectof the present invention to provide novel and improved methods and meansfor the production of synthetic single crystals of quartz.

Another object of the invention is the provision of extra-length Y-bartype synthetic quartz crystals and seeds.

. Still another object of the invention resides in the provision of amethod for uniting individual quartz crystal "seeds with .axes alignedin the Y-directio'n to form single seeds of extra-length from whichsingle Y bar crystals of comparable length may be grown.

A further object of the invention is to provide novel and improvedmethods for the synthesizing of quartz crystals wherein a higherpercentage of quartz usable for crystal plate fabrication is obtained onthe grown crys- 'tals.

A further object of the invention is the provision of novel methods ofsynthesizing quartz single crystals which may be more quickly, easily,and less-expensively fabricated into crystal plates.

These and ancillary objects of the invention and the manner of theiraccomplishment will be clearly apparent to those conversant with the artfrom a reading of the following description and subjoined claims inconjunction with the annexed drawing wherein like reference charactersdenote like parts throughout the several views and wherein,

Figure 1 is a perspective elevational view of a pair of quartz Y-barseed bodies fastened together and immobilized by a crystal splint, inthe manner of the presem invention;

Figure 2 is a view similar to Figure 1 showing the same seeds afterhaving been subjected to a conventional cryst'al-growing environment;

Figure 3 is a view similar to Figures 1 and 2 showing the same seedssubsequent to trimming; and

Figure 4 is a perspective elevational view of a composite Y-b'ar crystalgrown in accordance with the precepts of the present invention. I

Referring now to the drawings, Figure 1 shows a pair of conventionalY-bar seed bodies and 12 each having its Y crystal axis so designated.The seed bodies are necessarily of the same handedness and preferablyare Each of the seed bodies which, in any practical application of theinvention foreseen at the present time would be substantially identical,is in the form of an elongated rectangular parallelepiped havingmutually perpendicular pairs of substantially parallel majorlongitudinal surfaces designated by reference numerals 14, 16, 18, and20 for seed body 10 and 14', 16, 18', and 20 for seed body 12. Forpurposes of the present disclosure faces 14 and 18 of seed body 10 and14 and 18' of seed body 12 are arbitrarily designated the Z surfaces ofthe crystal, i.e., surfaces perpendicular to the Z crystal axis, while16, 20, 16' and 20' are X surfaces, being perpendicular to'the X crystalaxis. The X, Y and Z crystal axes, appropriate ly marked, are shown inFigures 1, 2 and 3 of the draw ing. It is pointed out at this time as amatter of importance that Y-bar seeds grow fastest and at the same rateon both Z surfaces, and at a slower and dissimilar rate on respective +Xand X faces.

In general practice of the invention, seed bodies 10 and 12 would beabout 6 inches long and about .04 square inch in cross section. The endsto be joined are suitably trimmed to provide complementary end surfacesthereon and with the seed bodies 10 and 12 thus pre-' ment as possible.Due to the difference in growth rates or the X+ and X- surfaces of theseed bodies, the corresponding ones of these surfaces should be matchedwhen the seed bodies are aligned. A simple and expeditious method foraccomplishing this important alignment of atomic planes and surfaces ispart of the disclosure of United States Letters Patent No. 2,914,383issued on the application of W. H. Charbonnet, Serial No. 511,614, filedon even date herewith and assigned to the same assignee as'the presentinvention.

With the seed bodies aligned as described above, the next step of thenovel process is to immobilize the mating ends of the bodies so as topreclude any relative movement thereof in order that they be maintainedin the same relative position throughout the growing process.

In the present illustrative embodiment of the invention this isaccomplished by means of one or more splints, two being shown at 24 and26, which are placed on opposite surfaces, either X or Z, of the seedbodies overlapping equally on both sides of the interface 22 between theabutting ends thereof.

.Splints 24 and 26 take the form of quartz crystal plates suitablyshaped to conform to the surfaces on which they are disposed and aresecurely fastened in position as by binding with numerous turns ofsilver wire 28, or equivalent means.

The seed bars, so prepared and appearing as shown in Figure 1, areplaced in any suitable seed holder and subjected to a chemical andphysical environment 'conducive to crystal growth. Ordinarily, growth ofthe crystal would be accomplished under conditions of high temperatureand pressure in an autoclave as described in United States LettersPatent 2,675,303 referred to herein'above but it is to be understoodthat any operative method and apparatus for growing synthetic quartzcrystals presently known or hereinafter discovered may be availed of.

After a suitable growing period, for example about 6 weeks, the splicedseed bodies will have grown together to form an integral piece of quartzsubstantially as shown in Figure 2. It will be noted that the interface22 may still be in evidence and the splint plates 24 and 26 havepartially dissolved and assumed an irregular shape partly merged withbut for the most part discernibly distinct from the seed bars. On thefree ends of the seed bars the characteristic rhombohedral and prismfaces 30 have started to form and the entire composite seed has beenenlarged by growth on the exposed surfaces.

The new growth on the spliced seed, as it appears in Figure 2 is trimmedby cutting and/ or lapping to remove all irregularities and unevennessso as to produce an elongated composite seed bar with smooth flatsurfaces substantially as shown in Figure 3. From this figure it will beclearly evident that the composite seed bar 1012 is similar to a singleY-bar seed cut from a single crystal except for its dimensions, itslength being approximately twice that of the single bar, and thepresence of a visible remanent of the joint at the interface 22.

The composite seed, so prepared and appearing gem erally as shown inFigure 3 is once again subjected to conditions conducive to crystalgrowth and allowed to grow for a substantial period of time, forexample, about 6 weeks or until suificient growth has taken place topermit cutting extra-length seeds from the crystal. At this stage, thecrystal appears generally as shown in Figure 4. It will be noted thatthe joint at interface 22 (shown in dotted line) is substantiallycoextensive with the cross-section of the two original seed bars 10 and12 and may appear as a cleavage plane in the composite crystal. The newgrowth, however, is continuous over the entire length of the crystal anddisplays no discontinuity due to the presence of the joint in thecomposite jse'ed bar. 1 p

, While satisfactory AT cut plates can now be cut from the extendedlength crystal, the initial crystal would logically be used as a sourceof extra-length seed bars which could be grown in any conventionalmanner to produce additional extra-length crystals. It will be apparentthat a single extra-long crystal obtained from spliced Y-bar seeds asdescribed above would be the unlimited source of any desired number ofextra-length seeds. Thus, the splicing procedure need be carried outonly once to obtain seeds twice the usual length. Seeds of greater thandouble length can be obtained either by splicing two or more doublelength seeds in the same manner as already described or by splicing anyreasonable number of conventional length seeds in the first instance. Inthis connection, it is pointed out that while the above description hasbeen concerned with the joining of the two seeds, this has been merelyfor convenience of illustration and description and that the inventionis in no way limited as to the number of'seeds which are spliced,originally or subsequently.

The advantages of extra-length seeds and crystals are of great economicimportance. The longer seeds simplify the process of loading autoclavesby reducing the number of individual seeds whichmust be prepared forgrowing and loaded into seed holders. able space within the autoclavemay be more efiiciently utilized, less volume being occupied by seedholders thus allowing an increase in the volume of seed materialand witha concomitant increase in the yield of quartz per autoclave run.

The longer crystals greatly reduce the amount of set up time required tocut a given number of plates as already explained above and effectimportant reductions in the amount of waste material per crystal.

be approximately 6 inches in total length as grown. In cutting thecrystal into plates the unusable ends bearing the rhombohedral and prismfaces are trimmed ofi, leaving a block of crystal about four inches longfor fabrication into plates. Thus, up to about 33% of a 6-inch Y-barcrystal is waste. A 12-inch Y-bar still has only two ends, and the 2inches of waste material resulting therefrom constitutes only about 17%of the crystal length. As the length of the crystal increases, thepercentage of waste becomes more and more insignificant. Of equalimportance is the fact that increasingly larger numbers of plates can becut for each crystal-mounting and set-up procedure. Therefore, thelonger crystals would be of advantage even if the increase in percentageof usable material is disregarded.

The length of seeds which may be evolved from repeated splicing ofY-bars according to the present in- In addition, the avail- For example,a conventional synthetic quartz Y-bar crystal may vention is limitedonly by practical considerations involved in handling, growing, cutting,etc.

While there has been described what at present is believed to be thepreferred embodiment of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is aimed,therefore, to cover in the appended claims all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A method of splicing quartz-crystal Y-bar seed bodies comprising:disposing the seed bodies to be joined in end-to-end abutment with theircorresponding atomic planes aligned; splinting the joint between saidseed bodies with crystal so as to preclude relative movementtherebetween; and exposing said seed bodies so splinted to a chemicaland physical environment conducive to crystal growth until the seedbodies and splinting crystal have grown together.

2. A method of growing extra lengthsynthetic single crystals of quartzcomprising: disposing a plurality of 'Y-bar seed bodies cut from thesame crystal in end-toend abutment with their Y crystal axes aligned andcorresponding major longitudinal faces matched and disposed in commonplanes; splinting the joint with crystal; exposing said seed bodies,while so disposed and maintained, to conditions conducive to crystalgrowth until said seed bodies have grown together into a single com-References Cited in the file of this patent UNITED STATES PATENTS1,958,014 Nicolson May 8, 1934 2,047,252 Bloomenthal July 14,19362,546,305 Jafie et al. .....I Mar. 27, 1951 2,674,520 Sobek etal. Apr.6, 1954 2,675,303 Sobek Apr. 13, 1954 OTHER REFER EN CES Beane: MarconiReview," v01. XVI, #111, 4th Quarter, 1953, pages and 158.

1. A METHOD OF SPLICING QUARTZ-CRYSTAL Y-BAR SEED BODIES COMPRISING:DISPOSING THE SEED BODIES TO BE JOINED IN END-TO-END ABUTMENT WITH THEIRCORRESPONDING ATOMIC PLANES, ALIGNED, SPLINTING THE JOIJNT BETWEEN SAIDSEED BODIES WITH CRYSTAL SO AS TO PRECLUDE RELATIVE MOVEMENTTHEREBETWEEN, AND EXPOSING SAID SEED BODIES SO SPLINTED TO A CHEMICALAND PHYSICAL ENVIRONMENT CONDUCTIVE TO CRYSTAL GROWTH UNTIL THE SEEDBODIES AND SPLINTING CRYSTAL HAVE GROWN TOGETHER.